1. Field of the Invention
This invention relates to the measurement of objects using an optical measuring system. More particularly, the invention relates to a method of measuring the lengths of spent nuclear fuel rods so that the mass of the rods can be determined.
2. Discussion of Prior Art
In the reprocessing of spent nuclear fuel it is important for inventory and accounting purposes that the amount of spent fuel to be reprocessed is calculated accurately. This requires a system for obtaining the mass of the spent fuel rods to be reprocessed.
In one particular application, measurement of the mass of the fuel rods takes place in a decanning cave in which a metal cladding is stripped from fuel elements to provide fuel rods for subsequent reprocessing. Because of the hostile environment existing within the cave, systems for direct weighing of the fuel rods have many disadvantages. For example, the components of such a system are subjected to adverse conditions of radiation, heat, mechanical shock and water existing within the cave. Thus, these systems tend to have a short operational life and require frequent servicing and maintenance. Because of the inaccessibility and the danger of radiation exposure associated with handling the weighing system components in the cave, direct weighing systems are unsatisfactory.
One known type of direct weighing system has a weighing device in which a weighing platform is supported on solid state load cells located in the decanning cave. Although such a system can produce accurate results, it has not proved satisfactory because the load cells are unable to withstand the mechanical shock loads and the high radiation fields existing within the cave and so tend to fail after a short period of time.